The History and Philosophy of AstronomyPhilosophy of Science: Two Traditions 1) Aristotle 2)...
Transcript of The History and Philosophy of AstronomyPhilosophy of Science: Two Traditions 1) Aristotle 2)...
The History and Philosophyof Astronomy
(Lecture 11: Galileo I)
Instructor: Volker BrommTA: Jarrett Johnson
The University of Texas at Austin
Astronomy 350L
(Fall 2006)
Galileo Galilei: The First Scientist
• 1564 (Pisa) – 1642 (Arcetri)
• founder of modern physics- law of inertia- law of free fall
• first astronomer to use telescope
• The “Trial of Galileo”(conflict with Catholic Church)
Galileo: Timeline and Context
• between Copernicus and Newton
• contemporary of Kepler and Tycho
Born in Pisa (1564)
• Pisa: part of Grandduchyof Tuscany
• University town
Professor in Pisa (1589-92)
• Professor of mathematics (badly paid)
• New laws of motion (inertia, free fall)
Philosophy of Science: Two Traditions
2) Archimedes1) Aristotle
(287-212 BC)
Archimedes of Syracuse (287 – 212 BC)
“Give me a place to stand,and I will move the Earth”
• eminent engineer, mathematician, and scientist!
Philosophy of Science: Two Traditions
2) Archimedes1) Aristotle
• philosophy mostimportant
• mathematics secondary• “laws” of nature
based on commonsense and intuition
• unlimited scope• truth by arguing itsplausibility
• search for causes
• physics mostimportant
• mathematics essential• laws of nature
based on simplemathematical principles
• limited scope• truth by experience(carry out experiments)
• Galileo strongly follows Archimedean tradition!
Professor in Pisa: Laws of Free Fall
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• Galileo: If friction from air can be ignored,all objects reach ground at same instant, with thesame speed constant acceleration (“one g”)
Professor in Pisa: Laws of Free Fall
• Galileo’ s trick: Slow down gravity!
• Experiment with inclined planes!
Professor in Pisa: Laws of Free Fall
• Galileo didn’t have precise clock
• Idea: Use little bells!
Professor in Pisa: Laws of Free Fall
Galileo’s Law of Free-fall
Earth’s Gravity (1 g)
Professor in Pisa: Law of Inertia
Gedanken Experiment (thought experiment)
• Law of inertia: Bodies remain at rest or in a stateof linear uniform motion, unless acted upon by force!
Law of Inertia: Implication for Astronomy
moving Earth:
• Motion of Earth is entirely plausible!• Aristotelian theory of motion is wrong!
moving ship:
Great Summary: Discorsi (Two New Sciences)
• Discorsi(The Two New Sciences, 1638)
• first modern scientific textbook
• laws of motion (inertia, free fall)
• sets out scientific method
Galileo’s role in the Scientific Revolution
Newton (1642-1727)- dynamics- law of gravity
Kepler (1571-1630)- celestial motion- 3rd Law
Galileo (1564-1642)- laws of free-fall- principle of inertia
“Standing on the shoulders of giants”
Professor in Padua (1592-1610)
• Professor of mathematics (much better paid)• Padua: one of most prestigious and oldest
universities in Europe
Padua and Venice (1592-1610)
• Padua: part of great freeRebublic of Venice
• Galileo’s Golden Time
Padua and Venice: Personal Life
• Longterm relationshipwith Marina Gamba (Venice)
• 3 daughters, 1 son
• “Galileo’s Daughther”:Sister Maria Celeste
The Invention of the Telescope (1609)
Hans Lippershey
• Telescope was invented in the Netherlands
Invention of the Telescope: Basic Idea
• Combine two curved lenses (convex or concave)!
Galilean Design (convex + concave)
Keplerian Design (convex + convex)
Galileo’s Discoveries with the Telescope
• Galileo constructs his own telescope!
Galileo’s Discoveries with the Telescope
• Galileo the Great Propagandist!
Galileo and the Telescope: The Moon
• Mountains and valleys! Not a perfect, smooth surface! • Aristotle is wrong!
Galileo and the Telescope: Sunspots
• Blemishes on the Sun! Not a perfect, smooth surface! • Aristotle is wrong!
Galileo and the Telescope: Moons of Jupiter
• Fours satellites (moons) around another planet! • Earth’s Moon not an anomaly anymore!
4 Galilean (Medicean) moons
Galileo and the Telescope: Moons of Jupiter
• Miniature model of the Solar System! • Crucial support for Copernican model:
- new satellites definitively don’t orbit Earth!- remove anomaly of Earth’s Moon
Galileo and the Telescope: Phases of Venus
• Galileo sees full cycle of phases! • One of the most important discoveries of astronomy!• Why???
Galileo and the Telescope: Phases of Venus
• Definitive proof for Copernican model of Solar System!
• But (to be honest): Tycho’s model can explain it, too!
Galileo and the Telescope: Phases of Venus
• Galileo the Great Salesman (he creates suspense)! • Delayed release of his discoveries: Attempt to secure
his priority!
A riddle for Kepler:
“Haec immatura a me jam frustra legunturO y”
“Cynthiae figuras aemulatur mater amorum”(Venus emulates the phases of the Moon)
Galileo and the Telescope: Nature of Milky Way
• With telescope: Many more stars become visible! • Stars appear as points • Thus, Tycho’s argument against Copernican model
not valid (stars can be very far away!)
Sidereus Nuncius (The Starry Messenger)
• Sidereus Nuncius(Starry Messenger, 1610)
• describes new astronomicaldiscoveries made withtelescope
• Galileo makes sure that hisfame would spread
• Earns him long-desiredappointment in Florence
Galileo and the Medici
• Cosimo II, Grand Dukeof Tuscany
• Galileo appointedCourt Mathematician
• No more teaching,generous salary
Galileo’s Return to Florence (1610-42)
• After leaving Padua/Venice, he slowly gets intocrosshairs of Roman Inquisition trial of 1633
Galileo (part 1)
• Galileo Galilei: - founder of modern physics- laws of free fall and inertia- established scientific method based on exeriments
• Starry Messenger (Telescopic Discoveries)- Phases of Venus: Proves Copernican model- Sunspots and mountains on the Moon:
celestial objects are not perfect and immutable- Moons of Jupiter
• Return to Florence - confrontation with Catholic Church begins to gather